1. Field of the Invention
This invention relates to a system for detecting or discriminating malfunction of an internal combustion engine radiator, more particularly to a system for detecting or discriminating malfunction of a radiator thermostat.
2. Description of the Related Art
The internal combustion engine of a vehicle is connected through a communicating passage with a radiator for cooling a coolant. A thermostat (a shut-off valve) is installed in the communicating passage. The thermostat closes the communicating passage when the coolant temperature is low, such as at engine starting, and opens it when the temperature rises so as to pass coolant into the radiator for cooling.
The radiator is one of the on-board components of a vehicle. The ability to detect or discriminate radiator malfunction is therefore desirable. It was for this purpose that the assignee developed a system that first checks whether the engine is in a state cooled to a temperature equal to the outside air temperature (intake air temperature) owing to thorough soaking (long-period or sufficient standing) and whether change in the outside air temperature since engine starting is small, then, when these conditions are met decides that the conditions for execution of malfunction detection have been established, whereafter it carries out a calculation for estimating the coolant temperature and decides that the radiator, more precisely the radiator thermostat, is faulty if, for example, the detected coolant temperature has not reached the judge-normal value when the estimated coolant temperature reaches the judge-malfunction value. This technology is described in the assignee""s Japanese Laid-Open Patent Application 2000-8853.
However, when the outside air temperature sensor is installed in the intake manifold for convenience of layout, the value of the air temperature detected by the air temperature sensor may be higher than the actual air temperature even when the vehicle has thoroughly soaked because of heat accumulated in the intake manifold owing to sun exposure. In such a case, the sensor detection value may decline sharply immediately after engine starting due to the intake of air under the high-load operation at this time. In addition, heat in the intake manifold may also make it impossible for the sensor detection value to accurately track the air temperature when the rate of air temperature decline is high. In this case, too, the sensor detection value may decline sharply immediately after engine starting due to the intake of air under the high-load operation at this time.
When the value of the outside air temperature detected by the air temperature sensor declines sharply during the high-load operation immediately after engine starting in this way, the conventional system is liable to judge that the conditions for execution of radiator malfunction detection have not been established. However, the sharp decline in the sensor detection value is a transient or momentary phenomenon caused by dispersion of the heat in the intake manifold and is not a substantial hindrance to malfunction detection or discrimination.
An object of this invention is therefore to offer an improvement on the assignee""s earlier developed technology, specifically to provide a system for detecting or discriminating malfunction of an internal combustion engine radiator that enables highly accurate detection or discrimination of internal engine radiator malfunction and that inhibits or prevents a decision finding that conditions for execution of malfunction detection or discrimination are not established when dispersion of the heat in the intake manifold installed with the outside air temperature sensor causes a transient or momentary decline in the outside air temperature sensor detection value during high-load operation immediately after engine starting.
The present invention achieves the object by providing a system for discriminating malfunction of a radiator having an inlet pipe connected to an internal combustion engine and a thermostat fitted in the inlet pipe (communicating passage) to open the inlet pipe to pass engine coolant in the radiator to cool, comprising: engine operating condition detecting means for detecting operating conditions of the engine including at least an outside air temperature and a coolant temperature; outside air temperature decline amount calculating means for calculating a decline amount of the detected outside air temperature since starting of the engine; malfunction discrimination execution condition establishing deciding means for comparing the calculated decline amount of the detected outside air temperature with a threshold value and for making a decision that conditions for execution of malfunction discrimination of the radiator are established, when the calculated decline amount of the detected outside air temperature is less than the threshold value; estimated coolant temperature calculating means for calculating an estimated coolant temperature based on at least the detected coolant temperature and a thermal load parameter contributing to coolant temperature rise, when the malfunction discrimination execution condition establishing deciding means makes the decision that the conditions are established; and malfunction discrimination executing means for comparing the estimated coolant temperature and the detected coolant temperature with predetermined values and for discriminating whether the radiator has malfunctioned based on results of comparison; wherein the improvement comprises: malfunction discrimination execution condition non-establishing preventing means for preventing the malfunction discrimination execution condition establishing deciding means from making the decision that the conditions are not established, utilizing a parameter related to a quantity of intake air.